Whatever a yogi observes,
He should view it as like an illusion.
Similar to a reflection in a mirror,
A dream, a mirage, a water-bubble,
Or a trick of the eye, so should he see it.
[The Buddha] said that is the main [insight].

arya nagarjuna

Excerpt from Arya Nagarjuna's Five Stages of Guhyasamaja. Quoted by His Eminence Choden Rinpoche to his disciples, before entering his final state of meditation at the Sera Jey Monastery, September 11, 2015.